The three most important Parameters which defines the pulp are. 1.)
Fiber Length, 2.) Brightness, 3.) Pulping process used.
e.g. Northern Soft Wood Bleached Kraft (NSWBK). The Northern Soft Wood tells it
is long fiber pulp. Bleached tells, it has high brightness and Kraft tells that
Kraft (Sulfate) pulping process is used to produced this pulp. Similarly
Southern Hard Wood Unbleached Kraft, will be a short fiber wood unbleached (low
brightness) pulp made by kraft process. Link to a few typical Market Pulp
data sheets.

Ash content in pulp may consists of various chemicals used during
pulping/bleaching, mineral matter from wood or metallic matter from pipes
and other machinery. It is not important parameter of
pulp.

Ash is the residue left after igniting pulp at 525 0C (As per TAPPI
T 211). Ash is reported in % of residue to dry pulp basis.

The standard procedure of measuring ash content is laid out in
TAPPI
T 211, ISO 1762

Brightness of Pulp

Brightness of paper is discussed in
Paper Properties. The paper brightness is mainly dictated by pulp
brightness. There are some modification in stock preparation which can alter
paper brightness to some extent such as filler, sizing, whitening agent,
dying etc.

Coarseness of Pulp

This is a measure of the average weight of fiber per unit length, often reported in units of mg/m. It is most conveniently measured
using an optical analyzer. For fibers of a given average length, it is a measure of the cross sectional area of the fiber. For a given average diameter, it is
measure of wall thickness. Coarse fibers are considered to be less conformable than
fine fibers and do not bond as readily. Coarser fibers also result in fewer fibers per
mass of pulp, which has a significant impact on sheet formation and light scattering potential.

Conductivity of Pulp

Electrical grade papers such as cable paper, condenser tissue or
insulation paper etc., require very low conductivity to electricity. The
presence of metal ion more specifically iron ion contribute to pulp
conductivity The pulp used for electrical grades are washed with
demineralized water, beater or refiner use lava or other non-metallic bars
and contacting surfaces of all equipment are made of stainless steel.

Values for the conductivity of the water extract of the
pulp are expressed in µS/m.

S =
Siemen (SI unit of electric conductance) = 1 mho.

Dirt in Pulp

Dirt content of pulp particularly of recycled pulp is important for its
suitability to make fine paper. Dirt is any foreign material in pulp. TAPPI
defines dirt as foreign matter in a sheet which, when examined by reflected,
not transmitted light, has a marked contrasting color and has an equivalent
black area of 0.04 mm2 or more.

The standard procedure of measuring dirt content is laid out in
TAPPI T213

Drainage Time of Pulp

Here the drainage time of pulp is discussed in reference to market pulp
and/or unrefined pulp. The drainage time of pulp or freeness or slowness of
pulp is modified to have some desired properties in the paper, here that is
not discussed.

Drainage of unrefined pulp which is measured as freeness can give an
indication on : 1) Fiber Length of pulp, as long fiber pulps have more
freeness compared to short fiber pulps, 2) Damage to fiber during pulping,
bleaching or drying as short fibers or fines produced during pulping
operation, reduces pulp freeness, 3) Refining energy required to achieve
certain slowness during stock preparation.

The standard procedure of measuring pulp drainage is laid out in
TAPPI T221, T227, ISO 5267-1 and ISO 5267-2

Dry Content of Pulp

Consistency:
is the term used to describe solid content of pulp during pulp
processing. For pulp and paper maker this is the most important
process parameters. All equipments are designed to handle pulp at and up to
certain consistency. Pulp consistency is roughly divided in to three ranges:

Low Consistency: <5%

Medium Consistency: 5 - 15%

High Consistency: >15%

But more preciously actual consistency for these ranges in various unit
operation of papermaking are different.

Unit Operation

Actual Consistency

Low Consistency (LC) %

Medium Consistency (MC) %

High Consistency (HC) %

Repulping

<6.0

<12.0

12 - 28

Screening

<1.5

<4.5

-

Centrifugal Cleaning

<1.5

<2.5

2.5 - 6.0

Bleaching

-

10 - 15

25 - 35

Refining

3 - 6

10 - 15

28 - 35

Headbox

<1.0

-

>1.0

It is the desire of every pulp maker to keep pulp at the highest possible
consistency to minimize dilution water usage and which ends up as effluent.
Higher consistency also helps in reducing the bleaching chemical
consumption. But there are practical limitation of handling pulp at higher
consistency such as high viscosity which make pulp flow very
difficult.

The standard procedure of measuring pulp consistency (up to 25%) is laid out
in TAPPI T240.

Moisture Content of Market Pulp: is important from storage,
transportation and handling point of view. Most of the market pulp are sold,
stored, transported and used as air
dry. The useable part of pulp is dry fiber only, so the tendency is to
minimize the moisture content op pulp.

Small quantity of pulp is sold as wet lap also. Wet lap pulp is not dried
at source and transported at about 50% moisture content. It is feasible for
short distance transportation and if pulp is to be used immediately at user
end.

Extractives (Low Molecular Weight Carbohydrates) in Pulp

The low molecular carbohydrates indicates an extent of cellulose
degradation during pulping and bleaching process, which may effect pulp
strength and other properties. Pulp is treated with 1% hot NaOH solution for
one hour to estimate loss of yield due to extractives.

The standard procedure of measuring 1% Hot Alkali Solubility is laid out
in TAPPI T212

Fiber Diameter

The effect of fiber diameter, wall thickness and coarsenses on sheet
properties is rather complex and not clearly established. These qualities
primarily affect fiber flexibility. Fiber diameter may be expressed mean
cross section or ratio of wall thickness to diameter, sometime termed as
fiber density.

Length of fibers (arithmetic average, weighted average etc.) is one
of the most important parameters of pulp. Pulp strength is directly
proportional to fiber length and dictates its final use. A long fiber pulp
is good to blend with short fiber pulp to optimize on fiber cost, strength
and formation of paper. Softwood with pulps in general have longer fiber
compared to hard wood pulp. Pulp made from woods grown in cold climate in
general have longer fiber compared to wood grown in warmer climates.

Chemical pulps in general have higher fiber length compared to semi
chemical pulp and mechanical pulp, when made from same wood. More fibers get
damaged/shorten by mechanical action than chemical action.

There are several method to measure /report fiber length of pulp. The
'fiber length of pulp by projection' is described in TAPPI T232.
The 'fiber length of pulp by classification' is described in
TAPPI T233. "Fiber length of pulp and paper by automated optical
analyzer using polarized light' is described in TAPPI T271.

Fiber population is defined as the numbers of fibers per gram. It is
expressed as Millions fibers/gm.

Raw Material

Length (mm)

Width (mm)

Population
(Million/gm)

Eucalyptus

0.7

0.016

13-18

Acacia

0.7

0.016

13-18

Scandinavian Birch

1.1

8.0

Scandinavian Pine

3.0

1.5

Tropical Mixed Hardwood

0.9

0.004

5.0

Southern Pine

3.5

1.0

Fiber Strength

The fiber strength, that is, the intrinsic strength of a single fiber,
affects sheet strength, although sheet strength is more affected by fiber
bonding. The fiber strength is indicative of maximum strength obtainable
from a given pulp. The maximum strength is not achieved in practice
owing to the fact that interfiber bond is the determining factor. Fiber
strength is usually measured by zero spam tensile test.

Fines Content

An additional measure of pulp particle size is the percentage of fines.
This consists of particles measuring less than 0.2 mm in length as
measured by an optical analyzer, or the weight percentage of the P200
fraction obtained from a Bauer McNett classifier. Fines can have a
significant impact on processing, particularly with regard to filtering
or drainage operations. Fines content of a kraft pulp may be in the
range of 5–15%. For a groundwood mechanical pulp, the fines content may
exceed 40%.

Hemicelluloses in Pulp

Pulps differ in their content of hemicelluloses and in the chemical
composition of their hemicelluloses. Hemicellulose content of a pulp is an
indicator of chemical differences originating with the tree and is affected
by the pulping process used. Pulp with higher Hemicellulose content develop
strength faster upon beating/refining. Hemicellulose helps cellulose fibers
bonding. Softwood hemicellulose is much more effective in fiber bonding than
hardwood hemicellulose.

Pulp from wheat straw, cornstalks and other non-wood plant have
much higher hemicellulose content than wood pulp. Pulp which
contains too much hemicellulose hydrates too fast and loses freeness
before adequate strength is developed.

Kappa number is determination of relative hardness, bleachability or
degree of delignification of pulp. It is important parameter of unbleached
pulp which is to be bleached. Low Kappa pulps are easier to bleach. High Kappa pulps usually require more
energy in refining, but often produce stronger paper or board (particularly
with regard to tear strength).

A fully bleached pulp can have Kappa # as low as 1 and very high yield
pulp may have kappa # as high as 100. Typical kappa # of some pulps.

Kappa #

Hardwood Pulp for Bleaching

14 - 20

Softwood Pulp for Bleaching

20 - 30

Wood pulp to be used Unbleached

40 -100

The method to find kappa # of pulp is described in
TAPPI T236.

Lignin in Pulp

Commercial pulp range in lignin content from 1.0% for "soft
cook" chemical pulp, about 8% for "hard cook"
chemical pulp and up to 16% for semi-chemical pulp. In general lignin
affects the properties of pulp in adverse manner. Pulp with too high lignin
content are slow beating and show poor interfiber bonding and as a result,
produce sheets of low density and inferior strength. Stiffness increases
with increased lignin content.

Permanganate Number (K Number)

Chemical test performed on pulp to determine the degree of delignification.
There is a mathematical relationship between
K Number and Kappa Number.

Pulping Process

Though the pulping process used is directly not a pulp property but this
is one of the most important parameters used in specifying the pulp. As we
move from full mechanical to full chemical pulping process, strength
of pulp and bleachability improves. Strength improves due to less
degradation of fibers and bleachability as more lignin is removed in
chemical than mechanical pulping processes.

Yield: Pulp yield is mainly govern by the pulping process.
Mechanical pulping processes which provide high yield, retain almost all
constituents of wood. Lignin which is second highest to cellulose, does not
bond to itself or cellulose fibers as fibers do, don't contribute to any
bonding, resulting in weak pulp. Secondly lignin is brown in color and to
maintain high yield of bleached pulp, lignin is not removed during
bleaching, but only chemically modified.

An estimate of the specific energy requirement can be made
for a given type of pulp if the unrefined pulp freeness and the
target freeness level are known. By subtracting the target freeness
from the unrefined freeness, the total amount of freeness change is
calculated.

Values in following table can then be used to predict approximately how much energy should be required to achieve the desired freeness drop.

Furnish

Freeness Drop Net HP Day/Ton

Bleached Hardwood Kraft

60 - 100 ml

Bleached Softwood Kraft

20 - 40 ml

GWD

3 - 7 ml

OCC

40 - 70 ml

Mixed Office Waste

50 - 70 ml

Newsprint

20 - 35 ml

Tensile Strength of Pulp

This is not the tensile strength of individual fiber, which is even higher
than or comparable with steel. The tensile strength discussed here is
maximum strength of randomly oriented pulp fiber when formed in a sheet.
This tensile strength gives an indication of the maximum possible strength
of pulp beaten under ideal condition. This again an indication of what level
of tensile strength can be achieved in real paper making environment.

Viscosity of Pulp

Solution viscosity of a pulp gives an estimation of the average
degree
of polymerization of the cellulose fiber. So the viscosity indicate the
relative degradation of cellulose fiber during pulping /bleaching process.

Dissolving pulps
from wood, which contains a large proportion of alpha cellulose, give
higher viscosity values than paper pulps.

The standard procedure of measuring pulp viscosity is laid out in
TAPPI T230

Zero-Span Tensile

One way of measuring tensile strength of pulp is "zero span breaking
strength' described TAPPI T231. Zero-span tensile data determines the maximum strength of pulp fibers when beaten
under idealized laboratory conditions.

Zeta Potential

Zeta potential is the parameter that determines the electrical
interaction between particles, a high value, positive or negative, prevents
flocculation. Changes to zeta potential can affect retention values,
strength, pitch deposition and additive requirements. The zeta potential of
pulp and other particles in the process may vary for a number of reasons,
e.g. changes in refining, pH, pulp source, broke content and quantities of
additives used.

Some of the commonly used Pulp & Fiber Test

TAPPI Method number

Test

*Related ISO Method

*Related ASTM

T211

Ash in Wood, Pulp, Paper :(525oC)

1762

D1102

T234

Coarseness of Pulp Fibers

T240

Consistency

4119

T213

Dirt in Pulp

5350/1, 5350/2

T221

Drainage time of Pulp

5267-1, 5267-2

T232

Fiber Length by Projection

16065-1, 16065-2

T233

Fiber Length by Classification

16065-1, 16065-2

T271

Fiber Length by Automated Optical analyzer

T227

Freeness of Pulp (CSF)

5267/2

T236

Kappa Number

302

T200

Laboratory Beating (Valley Beater method)

5264

T248

Laboratory Beating (PFI Mill method)

5264/2

T220

Physical testing of Pulp Hand sheets

5270

T204

Solvent Extractives of Wood & Pulp

624

D1107, D1108

T259

Species Identification of Nonwood Plant Fibers

T230

Viscosity of Pulp (Capillary Viscometer method)

5351/1

T207

Water Solubility of Wood & Pulp

D1110

T231

Zero Span Breaking Strength (Dry)

15361

D5804

* “Related” does not imply “equivalence.” A “Related Standard” may be a standard for a similar
property, but this should not assume identical technical content or matching
results.